CBSE Class 11 Chemistry VBQs Redox Reactions

Question. Which of the following is redox reaction?
(a) Evaporation of H₂O
(b) Both oxidation and reduction
(c) H₂SO₄ with NaOH
(d) In atmosphere O₃ from O₂ by lightning
Answer. B

Question. Without losing its concentration, ZnCl₂ solution cannot be kept in contact with
(a) Pb
(b) Al
(c) Au
(d) Ag 
Answer. B

Question. What is the change in oxidation number of carbon in the following reaction?
CH_4(g) + 4Cl_2(g) → CCl_4(l) + 4HCl_(g)
(a) + 4 to + 4
(b) 0 to + 4
(c) – 4 to + 4
(d) 0 to – 4
Answer. C

Question. Which of the following reactions are disproportionation reactions?
(i) 2Cu⁺ → Cu²⁺  + Cu⁰
(ii) 3MnO₄^2– + 4H⁺ → 2MnO₄^– + MnO₂ + 2H₂O
(iii) 2KMnO₄   →   K₂MnO₄ + MnO₂ + O₂
(iv) 2MnO₄^– + 3Mn²⁺ + 2H₂O → 5MnO₂ + 4H⁺
Select the correct option from the following.
(a) (i) and (iv) only
(b) (i) and (ii) only
(c) (i), (ii) and (iii)
(d) (i), (iii) and (iv)
Answer. B

Question. The oxidation state of Cr in CrO₅ is
(a) –6
(b) +12
(c) +6
(d) +4
Answer. B

Question. The correct order of N-compounds in its decreasing order of oxidation states is
(a) HNO₃, NO, N₂, NH₄Cl
(b) HNO₃, NO, NH₄Cl, N₂
(c) HNO₃, NH₄Cl, NO, N₂
(d) NH₄Cl, N₂, NO, HNO₃ 
Answer. A

Question. For the redox reaction,MnO₄^– + C₂O₄^2– + H⁺ → Mn²⁺ + CO₂ + H₂O
The correct coefficients of the reactants for the balanced equation are
    MnO₄ ^–   C₂O₄ ^2–     H⁺
(a) 16          5               2
(b) 2           5              16
(c) 2           16              5
(d) 5           16              2 
Answer. B

Question. Hot concentrated sulphuric acid is a moderately strong oxidizing agent. Which of the following reactions does not show oxidizing behaviour?
(a) Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O
(b) S + 2H₂SO₄ → 3SO₂ + 2H₂O
(c) C + 2H₂SO₄ → CO₂ + 2SO₂ + 2H₂O
(d) CaF₂ + H₂SO₄ → CaSO₄ + 2HF 
Answer. D

Question. (I) H_2O2 + O₃ → H₂O + 2O₂
(II) H₂O2 + Ag₂O →2Ag + H₂O + O₂
Role of hydrogen peroxide in the above reactions is respectively
(a) oxidizing in (I) and reducing in (II)
(b) reducing in (I) and oxidizing in (II)
(c) reducing in (I) and (II)
(d) oxidizing in (I) and (II) 
Answer. C

Question. The pair of compounds that can exist together is
(a) FeCl₃, SnCl₂
(b) HgCl₂, SnCl₂
(c) FeCl₂, SnCl₂
(d) FeCl₃, KI 
Answer. C

Question. A mixture of potassium chlorate, oxalic acid and sulphuric acid is heated. During the reaction which element undergoes maximum change in the oxidation number?
(a) S
(b) H
(c) Cl
(d) C 
Answer. C

Question. Oxidation numbers of P in PO₄^3–, of S in SO₄^2– and that of Cr in Cr₂O₇ ^2– are respectively
(a) +3, +6 and +5
(b) +5, +3 and +6
(c) –3, +6 and +6
(d) +5, +6 and +6
Answer. D

Question. Number of moles of MnO₄^– required to oxidize one mole of ferrous oxalate completely in acidic medium will be
(a) 7.5 moles
(b) 0.2 moles
(c) 0.6 moles
(d) 0.4 moles. 
Answer. D

Question. Which is the best description of the behaviour of bromine in the reaction given below?
H₂O + Br₂ → HOBr + HBr
(a) Proton acceptor only
(b) Both oxidised and reduced
(c) Oxidised only
(d) Reduced only 
Answer. C

Question. The oxidation states of sulphur in the anions SO₃^2–, S₂O^₄ 2– and S₂O₆^2– follow the order
(a) S₂O₄^2– < SO₃^2– < S₂O₆^2–
(b) SO₃^2– < S₂O₄^2– < S₂O₆^2–
(c) S₂O₄^2– < S₂O₆^2– < SO₃^2–
(d) S₂O₆^2– < S₂O₄^2– < SO₃
Answer. A

Question. Oxidation state of Fe in Fe₃O₄ is
(a) 5/4
(b) 4/5
(c) 3/2
(d) 8/3
Answer. D

Question. Reaction of sodium thiosulphate with iodine gives
(a) tetrathionate ion
(b) sulphide ion
(c) sulphate ion
(d) sulphite ion. 
Answer. A

Question. The oxide, which cannot act as a reducing agent is
(a) CO₂
(b) ClO₂
(c) NO₂
(d) SO₂
Answer. A

Question. Which substance is serving as a reducing agent in the following reaction?
14H+ + Cr₂O₇^2– + 3Ni → 7H₂O + 2Cr³⁺ + 3Ni²⁺
(a) H⁺
(b) Cr₂O₇^2–
(c) H₂O
(d) Ni 
Answer. D

Question. The oxidation state of I in H₄IO₆^– is
(a) + 1
(b) – 1
(c) + 7
(d) + 5
Answer. C

Question. Redox reactions are involved in chemical, industrial and biological processes. When the chemistry teacher taught the redox reactions with reference to electrochemical cells the students were not able to grasp the relation between anode, cathode, oxidation and reduction. To convince the students the teacher told them to remember the sequence English alphabets.
(a) How is sequence of English alphabets helpful to know the electrodes where oxidation and reduction take place?
(b) Write the associated value this problem.

Question. Fuels acts as source of energy. In the selection of fuel, its calorific value, economy and environmental effects are taken in to consideration. Hydrogen gas is such a fuel which has high calorific value and its combustion product does not have any harmful environmental effect. Still hydrogen is not suitable as domestic fuel.
(a) Why is hydrogen not considered as a suitable domestic fuel.
(b) Write the combustion reaction of hydrogen.
(c) Name device where hydrogen and oxygen are used to produce energy.
(d) Mention the associated value with this question.

Question. Yash Pal was totally confused to learn that phosphorous acid can act both as oxidizing agent as well as reducing agent while phosphoric acid is only an oxidizing agent. He discussed this problem with his friend Akbar. Akbar explained the phenomenon to his satisfaction.
(a) What examination did Akbar give to Yash Pal?
(b) in the reaction :-MnO₂ + 4HCl ⟶ MnCl₂ + 2H₂O +Cl₂
(c) What values are attached to this explanation?

Question. A solution of an electrolyte can be stored in a particular vessel only in case there is no chemical reaction taking place with the material of the vessel. The teacher asked a student Achin, is it possible to store silver nitrate in copper vessel. Achin explained the teacher; it is not possible to store silver nitrate in copper vessel. Achin explained the teacher; it is not possible to store silver nitrate in copper vessel and gave his explanation.
(a) What explanation did Achin gave to his teacher.
(b) What is oxidation according to electronic Concept?
(c) What values displayed by Achin?